If a person is in a catabolic state or in need of energy, such as during fasting, most glucose-6-phosphate will be used for glycolysis.
Glycolysis is the breaking down of one glucose molecule (6 carbons) into two pyruvate molecules (3 carbons). During the process, a net of two ATPs and two NADHs are also produced.
The following animation, using ball-and-stick models, allows you to control the 3 steps of glycolysis.
3 steps of Glycolysis
1. Energy investment step – 2 ATP are added to the 6 carbon molecule.
2. Glucose Split – The 6 carbon molecule is split into two 3 carbon molecules.
3. Energy harvesting step – 1 NADH and 2 ATPs are produced from each 3 carbon molecule (there are two 3 carbon molecules formed from each glucose).
Thus, from a molecule of glucose, the harvesting step produces a total of four ATPs and two NADHs. Subtracting the harvesting from the investment step, the net output from one molecule of glucose is two ATPs and two NADHs.
The figure below shows the stages of glycolysis, as well as the transition reaction, citric acid cycle, and electron transport chain that are utilized by cells to produce energy. They are also the focus of the next 3 sections.
References & Links
Glycolysis Animation – http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html